<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo {
            background-color: orange;
        }
    </style>
</head>

<body>
    <!-- 有些操作需要页面上有这个元素才能进行操作，例如 focus() 获取父元素 -->
    <button id="btn">添加一个输入框</button>
    <script type="text/javascript">
        const btn = document.getElementById('btn')
        btn.onclick = () => {
            const input = document.createElement('input')

            input.className = 'demo'
            input.value = 99
            input.onclick = () => { alert(1) }
            // input.parentElement.style.background='skybule'
            console.log(input.parentElement);
            document.body.appendChild(input)

            input.focus()
            // input.parentElement.style.background='skybule'
            console.log(input.parentElement);
        }
    </script>
</body>

</html>